1. Field of the Invention
This invention relates to an electrostatic copying apparatus, more specifically to an electrostatic copying apparatus which, as required, can form an image on both surfaces of a copying paper sheet.
2. Description of the Prior Art
It is frequently desired to form an image on both surfaces of a copying paper sheet for saving copying papers and to reduce the number of documents to be preserved. This desire has been achieved in recent years by the development of an electrostatic copying apparatus of the type adapted for forming an image on both surfaces of a copying paper sheet as required.
A typical example of such an electrostatic copying apparatus includes a copying paper conveying passage, a copying paper feeding means for feeding a copying paper sheet to the paper conveying passage, a conveyance controlling means disposed adjacent to the downstream end of the paper conveying passage, a copying paper discharging passage extending from its upstream end adjacent to the downstream end of the conveyance controlling means, a copying paper reversing passage extending from its upstream end adjacent to the downstream end of the conveyance controlling means, a copying paper returning passage extending from its upstream end adjacent to the upstream end of the conveyance controlling means, a copying paper re-feeding passage, and a copying paper re-sending means for resending a copying paper returned through the paper returning passage to the paper conveying passage through the paper re-feeding passage. The conveyance controlling means comprises a lower movable guide member and an upper movable guide member defining a paper moving passage therebetween. The lower and upper movable guide members are adapted to be selectively held at a first position at which the downstream end of the paper conveying passage communicates with the upstream end of the paper discharging passage and a second position at which the downstream end of the paper conveying passage communicates with the upstream end of the paper reversing passage and the upstream end of the paper reversing passage communicates with the upstream end of the paper returning passage.
In this type of electrostatic copying apparatus, an image is formed on one surface of a copying paper sheet while it is conveyed through the paper conveying passage after being fed thereto from the paper feeding means. When it is desired to form an image only on one surface of the sheet, the sheet having one image formed on it is introduced into the paper discharging passage through the paper moving passage defined between the lower and upper movable guide members held at the first position, and then discharged through the paper discharging passage. On the other hand, when it is desired to form an image on both surfaces of the sheet, the aforesaid copying paper bearing an image on one surface is then introduced into the paper reversing passage through the paper moving passage defined between the lower and upper movable guide members held at the second position. After the trailing end of the paper sheet has passed the downstream end of the paper conveying passage, the moving direction of the paper sheet is reversed, and the sheet is introduced into the paper returning passage. The paper sheet is returned to the paper re-sending means through the paper returning passage. The sheet is re-fed to the paper conveying passage through the paper re-feeding passage from the paper re-sending means. During re-conveyance of the sheet through the paper conveying passage, an image is formed on the other surface of the paper. The sheet bearing an image on both surfaces is then introduced into the paper discharging passage through the paper moving passage between the lower and upper movable guide members held at the first position, and discharged through the paper discharging passage.
The aforesaid type of conventional electrostatic copying apparatus has not proved to be entirely satisfactory, and has various problems to be solved, for example with regard to the operation of removing copying paper that jams in various passages, the structure of the apparatus on the upstream side of the conveyance controlling means (and therefore on the downstream end of the paper conveying passage and the upstream end of the paper returning passage), the structure of the apparatus on the downstream side of the conveyance controlling means (and therefore the upstream end of the paper discharging passage and the upstream end of the paper reversing passage), and the structure of the paper returning passage.